Silica

ABSTRACT

Silanized, structurally modified, pyrogenically produced silicas, characterised by groups fixed to the surface, wherein the groups are dimethylsilyl and/or monomethylsilyl, are produced in that pyrogenically produced silica is treated by a known method with dimethyldichorosilane and/or monomethyltrichlorosilane, the groups dimethylsilyl and/or monomethylsilyl being fixed on the surface of the pyrogenic silica, and is then structurally modified and optionally post-ground. They are used to improve scratch resistance in lacquers.

The invention relates to a silanised, structurally modified, pyrogenically produced silica, a process for the production thereof and its use.

It is known to use nanoscale particles in transparent coating compositions.

Thus, according to U.S. Pat. No. 6,020,419, pyrogenically produced silicon dioxides, deagglomerated in situ, which have been made hydrophobic with dimethyldichlorosilane (Aerosil® R 972), are used in polyurethane lacquers to improve the scratch resistance of the coatings.

The known silica has the disadvantage that it cannot be produced in powder form without a lacquer binder.

The object therefore existed of developing a silica that does not have these disadvantages.

The present invention provides silanised, structurally modified, pyrogenically produced silicas, which are characterised by groups fixed on the surface, the groups being dimethylsilyl and/or monomethylsilyl, preferably dimethylsilyl.

In a preferred embodiment of the invention the silicas can have the following physico-chemical characteristics:

-   BET surface area m²/g: 25-400 -   Average size of the primary particles nm: 5-50 -   pH value: 3-10 -   Carbon content %: 0.1-10 -   DBP value %: <200

The silica according to the invention can have a tamped density of 100 to 280, preferably 100 to 240 g/l.

A tamped density of more than 280 g/l leads to poorer results in the technical lacquer tests.

Pyrogenic silicas are known from Winnacker-Küchler Chemische Technologie, volume 3 (1983) 4th edition, page 77 and Ullmanns Enzyklopädie der technischen Chemie, 4th edition (1982), volume 21, page 462.

In particular, pyrogenic silicas are produced by flame hydrolysis of vaporisable silicon compounds, such as e.g. SiCl₄, or organic silicon compounds, such as trichloromethylsilane.

The invention also provides a process for the production of the silanised, structurally modified, pyrogenically produced silicas according to the invention, which is characterised in that pyrogenically produced silica is treated with dimethyldichlorosilane and/or monomethyltrichlorosilane by a known method, the dimethylsilyl and/or monomethylsilyl groups being fixed on the surface of the pyrogenic silica, and is then structurally modified and optionally post-ground.

In one embodiment of the invention a tempering can take place after the structural modification and/or post-grinding.

The silicas according to the invention can be produced e.g. as follows:

The silicas, which can be produced as described in DE 1 163 784, are then structurally modified by mechanical action and possibly post-ground in a mill. A tempering can possibly take place after the structural modification and/or post-grinding.

The structural modification can take place e.g. with a ball mill or a continuously operating ball mill. The post-grinding can take place e.g. using an air-jet mill or pin mill. The tempering can take place batchwise, e.g. in a drying cupboard, or continuously, e.g. in a fluidised bed. The tempering can take place under protective gas, e.g. nitrogen.

The silicas according to the invention can be incorporated into lacquers, as a result of which these lacquers have increased scratch resistance.

EXAMPLES

Production and physico-chemical properties of the silicas

Production of the comparative silicas:

The production of the comparative silicas 1, 2 and 3 takes place as described in DE 1 163 784.

Production of the silicas according to the invention:

The silicas, which are produced as described in DE 1 163 784, are then structurally modified by mechanical action and possibly post-ground in a mill. A tempering can possibly take place after the structural modification and/or post-grinding.

The structural modification can take place e.g. with a ball mill or a continuously operating ball mill. The postgrinding can take place e.g. using an air-jet mill or pin mill. The tempering can take place batchwise, e.g. in a drying cupboard, or continuously, e.g. in a fluidised bed. The tempering can take place under protective gas, e.g. nitrogen. TABLE 1 Overview of the production of the comparative silicas and the silicas according to the invention (Examples) Post-grinding Surface-fixed structural after structural Temparing after Designation group modification modification post-grinding Comparative silica 1 Dimethylsilyl No — — Comparative silica 2 Dimethylsilyl No — — Comparative silica 3 Dimethylsilyl No — — Silica 1 Dimethylsilyl Yes No No Silica 2 Dimethylsilyl Yes No No Silica 3 Dimethylsilyl Yes No No Silica 4 Dimethylsilyl Yes No No Silica 5 Dimethylsilyl Yes Yes No Silica 6 Dimethylsilyl Yes No No Silica 7 Dimethylsilyl Yes Yes No Silica 8 Dimethylsilyl Yes Yes Yes Silica 9 Dimethylsilyl Yes Yes Yes Silica 10 Dimethylsilyl Yes Yes No Silica 11 Dimethylsilyl Yes Yes No

TABLE 2 Physico-chemical data of the silicas according to the invention (Examples) and the comparative silicas Temped Loss on Loss on C DHP HRT specific density dying ignition pH content; adsorption surface area Designation [g/l] [%] [%] value [%] [%] [m³g] Comparative 64 0.1 0.5 4.0 0.8 243 113 silica 1 Comparative 67 0.5 0.6 4.8 1.0 256 165 silica 2 Comparative 72 0.7 1.0 4.0 1.6 255 256 silica 3 Silica 1 236 0.1 0.6 4.0 0.8 127 115 Silica 2 204 0.1 0.6 3.9 0.8 137 116 Silica 3 223 0.3 0.7 4.2 1.0 160 169 Silica 4 186 0.3 0.7 4.2 1.1 152 171 Silica 5 109 0.2 0.7 4.4 1.1 159 167 Silica 6 193 1.2 0.7 5.2 1.7 157 258 Silica 7 125 0.2 0.7 4.1 0.8 130 110 Silica 8 108 0.7 1.3 5.0 1.7 156 257 Silica 9 123 0.3 0.5 4.3 1.1 157 165 Silica 10 102 0.7 1.2 6.2 1.7 164 256 Silica 11 160 0.2 0.7 4.0 0.8 132 115

Example 1

For the investigation of the improvement in scratch resistance, a conventional 2-component polyurethane lacquer was used. The formulation of the lacquer and its production, including application, are summarised below: Parts by wt. Millbase Acrylic copolymer, mod. with synthetic fatty 43.4 acids, 60% solution Butyl acetate 98% 17.8 xylene 3.9 AEROSIL 5.0 Σ 70.7 Lacquer make-up xylene 11.3 Ethoxypropyl acetate 3.4 Butyl glycol acetate 1.6 Aliphatic polyisocyanate, approx. 75% in 1- 18.6 methoxypropyl-2-acetate/xylene 1:1 Σ 105.0 Binder concentration: 40%

-   AEROSIL calculated on the basis of millbase (solids): 19.2% -   AEROSIL calculated on the basis of lacquer (total): 5.0% -   AEROSIL calculated on the basis of lacquer (solids): 12.5%

Production and application of the lacquers

The binder is mixed with the solvents. Then, for the

purpose of predispersion, the AEROSIL is incorporated into

this mixture with the high-speed mixer (disk Ø45 mm) and predispersed for 5 min at 2000 rpm. The mixture is dispersed in a laboratory pearl mill for 30 min at 2500 rpm and 60% pump capacity using glass beads (Øapprox. 1 mm). The millbase is tested with a grindometer, 25μm, in accordance with DIN ISO 1524. It must be smaller than 10μm.

The conversion of the millbase to lacquer takes place in accordance with the formulation, the components being mixed with a vane agitator at 2000 rpm. The hardener is incorporated in the same way.

After adjusting the lacquers to spray viscosity in accordance with DIN 53411, the lacquers are applied to black lacquered metal sheets, e.g. DT 36 (from Q-Panel), by spray application (coat thickness about 40-50 μm). After spraying, the metal sheets are dried for 24 h at room temperature and then for 2 h in a drying oven at 70° C. Scratch tests: The metal sheets are abraded with a quartz/water slurry (100 g water +1 g Marlon A 350, 0.25% +5 g Sikron F500) using an abrasion and washing resistance tester (Erichsen, brush with hog's bristles). The gloss before and 10 min after the abrading is determined with a reflectometer (20° irradiation angle). TABLE 3 Summary of the properties of the liquid lacquers relevant in terms of lacquer technology, and of the applied and dried films. Comparative Silica Silica Comparative Silica Silica silica 1 1 2 Reference silica 2 3 4 Reference Grindometer value [μm] <10 <10 <10 / <10 <10 <10 / Viscosity (millbase) [mPas]  6 rpm 4710 421 772 571 4990 802 772 55 60 rpm 1120 210 264 225 1200 279 264 52 Viscosity (lacquer + hardener) [mPas]  6 rpm 882 105 210 135 857 235 105 70 60 rpm 239 75 92 79 242 100 26 37 Flow Orange-peel OK OK OK Orange-peel OK OK OK Scratch resistance 20° reflectometer value 39.0 83.4 83.5 88.8 67.2 84.2 82.6 89.3 before scratching Haze before scratching 430 30 40 3 235 18 10 2 40 strokes with Sikron F 500 / 83.7 82.3 56.0 / 74.7 80.4 47.2 residual gloss [%]

The silicas 1 +2 and 3 +4 according to the invention can be used in high concentrations without impairing the appearance of the lacquer surface owing to their substantially lower rheological efficiency compared with comparative silicas 1 and 2. In addition, the silicas according to the invention display a substantial improvement in the scratch resistance of the lacquer surface.

Example 2

In this example the influence of the structural modification was investigated on the basis of a high solids 2-component PU clear lacquer. The formulation of the lacquer and its production, including application and testing, are summarised below: Parts by wt. Millbase Acrylic copolymer, mod. with synthetic 61.0 fatty acids, 70% in n-butyl acetate Butyl acetate 98% 7.3 Methoxypropyl acetate 1.7 Solvesso 100 2.0 xylene 2.0 Baysilon OL 17, 10% in xylene 0.7 (silicone oil) AEROSIL 5.0 Σ 79.7 Lacquer make-up (hardener) Aliphatic polyisocyanate, 90% in n- 22.3 butyl acetate Butyl acetate 98% 2.0 Solvesso 100 1.0 Σ 105.0 Binder concentration: 62.8%

-   Aerosil calculated on the basis of millbase (solids):11.7% -   Aerosil calculated on the basis of lacquer (total): 5.0% -   Aerosil calculated on the basis of lacquer (solids): 8.0%     Production and application of the lacquers

The binder is mixed with the solvents. Then, for the purpose of predispersion, the AEROSIL is incorporated into this mixture with the high-speed mixer (disk Ø45 mm) and predispersed for 5 min at 2000 rpm. The mixture is dispersed in a laboratory pearl mill for 30 min at 2500 rpm and 60% pump capacity using glass beads (Ø approx. 1 mm). The millbase is tested with a grindometer, 25 μm, in accordance with DIN ISO 1524. It must be smaller than 10 μm.

The conversion of the millbase to lacquer takes place in accordance with the formulation, the components being mixed with a vane agitator at 2000 rpm. The hardener is incorporated in the same way.

After adjusting the lacquers to spray viscosity in accordance with DIN 53411, the lacquers are applied to black lacquered metal sheets, e.g. DT 36 (from Q-Panel), by spray application (coat thickness about 40-50 μm). After spraying, the metal sheets are dried for 24 h at room temperature and then for 2 h in a drying oven at 70° C.

Scratch tests:

The metal sheets are abraded with a quartz/water slurry (100 g water +1 g Marlon A 350, 0.25% +5 g Sikron F500) using an abrasion and washing resistance tester (Erichsen, brush with hog's bristles). The gloss before and 10 min after the abrading is determined with a reflectometer (20 ° irradiation angle). TABLE 4 Summary of the properties of the liquid lacquers relevant in terms of lacquer technology, and of the applied and dried films. Comparative silica 2 Silica 3 Silica 4 Reference Grindometer value [μm] <10 <10 <10 / Viscosity (millbase) [mPas]  6 rpm 6200 1500 541 140 60 rpm 2100 900 559 195 Viscosity (lacquer + hardener) [mPas]  6 rpm 3821 1041 497 167 60 rpm 1320 666 446 195 Flow marked OK OK OK orange-peel 20° reflectometer value 81.0 83.5 82.8 88.0 before scratching Haze 25 5 6 2 40 strokes with Sikron 94.3 93.4 82.0 F 500 residual gloss [%]

The silicas 3+4 according to the invention can be used in high concentrations without impairing the appearance of the lacquer surface owing to their substantially lower rheological efficiency compared with comparative silica 2. In addition, the silicas according to the invention display a substantial improvement in the scratch resistance of the lacquer surface.

Example 3

Direct comparison of the silicas according to the invention with a scratch-resistant lacquer according to DE 198 11 790 A1, in which AEROSIL R 972 is used to improve the scratch resistance. Silicas 2) Prior according to art 1) the invention Millbase Desmophen A 2009/1 190.2 Methoxypropyl acetate: 36.8 Solvesso 100 1:1 AEROSIL 23.0 Σ 250.0 Lacquer make-up Desmophen A YEP4-55A, 96.0 — contains AEROSIL R 972 Millbase — 48.9 Desmophen 2009/1 — 24.9 OL 17, 10% in MPA — — Modaflow 1% in MPA — — MPA: Solvesso 100 1:1 11.6 33.8 Butyl glycol acetate 10.5 10.5 Byketol OK 7.5 7.5 Byk 141 0.8 0.8 Hardener addition Desmodur N 3390 23.6 23.6 Σ 150.0 150.0 Production and application of the lacquers

-   1) Comparative silica 1 is incorporated into the binder in     accordance with DE 198 11 790 Al using a jet disperser. -   2) The binder is mixed with the solvents. Then, for the purpose of     predispersion, the AEROSIL is incorporated into this mixture with     the high-speed mixer (disk Ø45 mm) and predispersed for 5 min at     2000 rpm. The mixture is dispersed in a laboratory pearl mill for 30     min at 2500 rpm and 60% pump capacity using glass beads (Øapprox. 1     mm). The millbase is tested with a grindometer, 25 μm, according to     DIN ISO 1524. It must be smaller than 10 μm.

The conversion to lacquer of the millbases corresponding to 1) or 2) takes place in accordance with the formulation, the components being mixed at 2000 rpm with a vane agitator. The hardener is incorporated in the same way.

After adjusting the lacquers to spray viscosity in accordance with DIN 53411, the lacquers are applied to black lacquered metal sheets, e.g. DT 36 (from Q-Panel), by spray application (coat thickness about 40-50 μm). After spraying, the metal sheets are dried for 24 h at room temperature and then for 2 h in a drying oven at 70° C.

Scratch tests:

The metal sheets are abraded with a quartz/water slurry (100 g water+1 g Marlon A 350, 0.25% +5 g Sikron F 500) using an abrasion and washing resistance tester (Erichsen, 5 brush with hog's bristles). The gloss before and 10 min after the abrading is determined with a reflectometer (20 ° irradiation angle). TABLE 5 Summary of the properties of the liquid lacquers relevant in terms of lacquer technology, and of the applied and dried films. Prior art Silica 1 Silica 4 Reference Grindometer value [μm] <10 <10 <10 / Viscosity (millbase) [mPas]  6 rpm 58 30 26 30 60 rpm 48 43 33 40 Wave scan long wave 4.8 1.2 1.1 1.4 short wave 6.5 3.0 3.1 4.7 20° reflectometer value 89.0 90.2 89.6 90.8 before scratching Haze before scratching 4 4 3 4 40 strokes with Sikron F 500 78.3 85.9 86.2 55.3 Residual gloss [%]

It is shown that a substantially better improvement in the residual gloss is achieved after a scratch stressing of the lacquer surface by using the silicas according to the invention than with the prior art. In addition, owing to their low rheological efficiency, the silicas according to the invention do not cause an orange-peel effect. 

1. Silanised, structurally modified, pyrogenically produced silicas, characterised by groups fixed to the surface, wherein the groups are dimethylsilyl and/or monomethylsilyl.
 2. Silanised, structurally modified, pyrogenically produced silicas according to claim 1, characterised by the following physico-chemical characteristics: BET surface area m²/g: 25-400 Average size of the primary particles nm: 5-50 pH value: 3-10 Carbon content %: 0.1-10 DBP value %: <200
 3. Process for the production of the silanised, structurally modified, pyrogenically produced silica according to claim 1, characterised in that pyrogenically produced silica is treated by a known method with dimethyldichlorosilane and/or monomethyltrichlorosilane, the groups dimethylsilyl and/or monomethylsilyl being fixed on the surface of the pyrogenic silica, and is then structurally modified and optionally post-ground.
 4. Process for the production of the silanised, structurally modified, pyrogenically produced silica according to claim 3, characterised in that a tempering takes place after the structural modification and/or post-grinding.
 5. Use of the silanised, structurally modified, pyrogenically produced silica to improve the scratch resistance of lacquers.
 6. A silanised, structurally modified, pyrogenically produced silica having groups fixed to the surface wherein said groups comprise at least one of dimethylsilyl and monomethylsilyl.
 7. The silanised, structurally modified, pyrogenically produced silica according to claim 6 having the following physical chemical properties: BET surface area m²/g: 25-400 Average size of the primary particles nm: 5-50 pH value: 3-10 Carbon content %: 0.1-10 DBP value %: <200
 8. The silanised, structurally modified, pyrogenically produced silica according to claim 6, which has a tamped density of 100 to 280 g/l.
 9. A process for the production of a silanised, structurally modified, pyrogenically produced silica of claim 6, comprising: treating a pyrogenically produced silica with at least one of dimethyldichlorosilane and monomethyltrichlorosilane to thereby fix groups on the surface of the pyrogenic silica, said groups being at least one of dimethylsilyl and monomethylsilyl, structurally modifying said silica and optionally post grinding said silica.
 10. The process according to claim 9, wherein structurally modifying is by mechanical action.
 11. The process according to claim 9, further comprising tempering after at least one of structurally modifying said silica and post grinding said silica.
 12. The process according to claim 10, wherein mechanical action is by ball milling.
 13. The process according to claim 7, wherein post grinding is by air-jet mill or pin mill.
 14. The process according to claim 11, wherein tempering takes place under protective gas.
 15. A lacquer comprising a polyurethane and the silanised silica according to claim
 6. 16. A surface coated with the lacquer according to claim
 15. 17. The surface according to claim 16, which is metal. 